There are no flyable fixed-wing planes in Grand Theft Auto IV on any platform. The game only features helicopters.
Dial on in-game phone: **359-555-0100** (Annihilator – armed helicopter). Note: Blocks achievements/trophies for that session.
Map size (Liberty City ≈ 8 km²) and engine streaming limits made fixed-wing flight impractical. GTA V (Los Santos ≈ 80 km²) was built for it.